Book Review

by Joseph H. Zernik, D.M.D., Ph.D. Department of Orthodontics University of Southern California

The current volume on Biomechanics, edited by Dr. Nanda, Chair of the Department of Orthodontics at the University of Connecticut, and arguably a leading center in formalizing biomechanics in orthodontics. The volume was produced at a very high quality, with a large number of diagrams and numerous color photographs of clinical cases demonstrating various treatment sequences. It is highly recommended for every orthodontic resident, although it may be somewhat difficult to digest before getting a good introductory class in biomechanics. It is equally recommended for the practicing orthodontist who strives to effectively treat also the more challenging cases.

This reviewer must qualify himself: As an alumnus of the Department of Orthodontics at the University of Connecticut, I feel honored and privileged to be called upon to review a book where two of my teachers, and my older and younger colleagues, alumni of the Department, who are mostly active in academic orthodontics, are contributors.

The first chapter, by Nanda and Kuhleberg provides a clear presentation of the basic approach to biomechanics in orthodontics pioneered by Dr. Burstone. This approach, utilizing a simple but effective model system for orthodontic tooth movement, analyzes orthodontic appliances based on the assumptions of equilibrium in static beam systems. Older approaches to biomechanics and orthodontic tooth movement included the implied, intuitive "stick in the mud" model, which was rather effective in explaining traditional Tweed mechanics. Indeed, the consequent "anchorage management" concept is still the predominant mode of thinking of practicing orthodontists. However, such older models systems, were relatively primitive, and did not generate significant analytical power. Moreover, these concepts were inherently tied to methods of treatment based on the use of stiff wires and heavy forces in a biomechanic approach that emphasized appliance-shape and detailed wire-bending techniques in driving the orthodontic treatment.

The biomechanical approach to orthodontic treatment, in similarity to Begg's technique, emphasized early on the use of continuous light forces and low friction systems in driving orthodontic tooth movement, and attempted to design appliances generating such forces using the various materials available at the time. This approach was taken to its next logical step in emphasizing the use of orthodontic wires of various moduli of elasticity in order to achieve differential tooth movement, and in particular - seeking methods to approach effective, highly elastic appliances. Thus, in some older publications, one can spot incredibly cumbersome, multiple helix, stainless-steel closing loops. The logic of such appliances is evident nowadays to anybody experienced in the use of nickel-titanium springs and wires, but was rather revolutionary at its time. Thus, the biomechanical approach to orthodontics is not necessarily tied to a specific appliance or treatment sequence, but more to a basic conceptual framework. This feature makes this approach more durable, and its long lasting influence in the field of orthodontics is increasingly apparent.

The limitations of this model system are clear, like any model system trying to reduce to several simple mechanical principles a complex series of biological tissue responses. Some of the limitations often mentioned involve the use of the equilibrium assumption on the orthodontic wire, as an approximation, but eventually presenting the system of forces and moments on the supporting dental segments and their alveolar support; our inability to clinically determining the actual center of resistance of a given tooth or dental segment, or to easily determine the magnitude of moments in a clinical situation.

Some clinically obvious phenomena are difficult to explain using this model system, for example, the phenomenon traditionally referred to as the "row-boat effect", where uprighting of the canines (or an anterior segment) excessively tipped into an extraction site results in protraction of the molars (or posterior segment) and "anchorage loss". Such a phenomenon indicates the generation of horizontal forces as side effects of a system intended only to generate pure moments on either segment. However, similar systems are most often analyzed in the biomechanical model as generating only vertical forces and vertical side effects.

This chapter is highly recommended to any resident in his first year in an orthodontics program, and to those teaching orthodontics as a standard text in undergraduate or graduate courses in orthodontics involving a systematic presentation of biomechanics.

Chapter 2 presents a systematic approach to orthodontic treatment planning, emphasizing VTO's or Visual Treatment Objectives, a term often used by Dr. Rickets. The approach presented here involves both mid-sagital and occlusal VTO's, the latter presented in the Occlusogram. In my years in teaching orthodontics and treatment planning with starting residents, I find this approach uniquely effective in educating our future orthodontists to perceive treatment planning in terms of a quantitatively realistic set of hard and soft tissues treatment goals, rather than an sequence of orthodontic appliances and the related standard justifications. Again, some older methods tried to approach the same issue, but in a much more crude and limited fashion, for example - the Steiner Chevrons.

Chapter 3 and 4 present studies into orthodontic materials, and the latter chapter, by Dr. Graber, provides an excellent review of the use of magnets in orthodontics. As a bone biologist, I must add that I support the skeptical side in the debate over the existence of any valid orthopedic or orthodontic effects to electrical currents or fields, covered here in detail. The chapter by Kusy et al. emphasizes the potential uses of surface modifications of orthodontic wires and brackets in producing effective new appliances.

The remaining chapters present the application of the same biomechanical approach to various clinical treatment situations, including several chapters on Class II treatment (but unfortunately none on Class III treatment, although the principles are similar), on treatment of impacted canines, space closure, and compromised, partially edentulous patients.

This book makes it obvious that the Department in Connecticut has produced over the years much more than its fair share of alumni who remained in academic orthodontics, at a time when lack of academics our field is a constant issue of concern. This must also be attributed to the educational model practiced in the Department in Connecticut. A superior facility, in a university supported by a generous public State system and led with clear academic standards and an excellent research environment, can become over the years a major resource for the profession. It is also clear that whereas other centers of influence may be best known for their emphasis on Growth and Development, or Clinical Studies of various clinical modalities, etc., the Department in Connecticut has been focusing for several decades on biomechanics.

The current volume, edited by Dr. Ravi Nanda, in its scope, diversity, and general approach, provides an excellent textbook in biomechanics, and is highly recommended as a standard teaching text in this field.

Joseph H. Zernik, D.M.D. Ph.D. Professor, Department of Orthodontics University of Southern California http://www-hsc.usc.edu/~jzernik/